Keywords: NE5532, TDA1521 power amplifier circuit diagram
Author: Mao Ruili
The megaphone is common, typical electronic products. Composed of DC voltage regulator, audio preamplifier, power amplifier three parts (as shown below). The megaphone basically covers all the contents of the amplified circuit, the comprehensive intelligence is strong, and each to part is a separate unit circuit. In this production, the audio preamplifier and power amplifier part are elaborated. Designed and produced, then add some auxiliary circuits, connect together, and debug. A megaphone that can be applied.
First, the production of audio preamplifiers
The output signal of the microphone typically only has about 5mV, so it is necessary to make an enlarged zoom in, this task is done by the preamplifier. The preamplifier requires a small distortion and the communication bandwidth. The main technical indicators are as follows. Voltage magnification: 10 times: passband: 50Hz ~ 20kHz.
1. Circuit design This project is designed and produced is most of a two-channel megaphone. Each channel includes two parts of the preamplifier and volume adjustment circuit. The front amplifier is implemented by integrated op amp, and volume control is implemented with a two-link. The circuit is shown below. Integrated amplifies NE5532. NE5532 is dual op amp, which belongs to high performance low noise op amp, which has better noise performance, excellent output driving capability and relatively high small signals and power bandwidth. The circuit is two in-phase input amplifying circuits, and the voltage amplification of the circuit is about 11 times by analysis, respectively corresponds to two channels. The 200K potentiometer in the figure is to ensure the same size of the two channels; the role of the double potentiometer is to adjust the size of the two channel output voltages, that is, the size of the two channel volumes; the effect of the regulator is guaranteed The voltage supplied from the power supply is 15V; the power supply capacitance is to eliminate the effect of ripple and high frequency noise, prevent self-excitation; input, the capacitance of the output is active.
2. When the circuit makes the welding circuit Note: (1) The two-unit potentiometer should not be fixed on the board, and should be fixed to the housing when assembled, as a knob that adjusts the volume. (2) In order to ensure the balance of the two channels, the feedback resistance of one of the amplifiers can be replaced with a 200KΩ potentiometer, and the two amplifier gain is equal to the value of the value of the potentiometer. 3. Circuit Debug Method (1) Two channel input inputs the same AC small signal (UI = 10mV, f = 1 kHz) to measure two output voltage, observe the range of output voltage variations; (2) Adjust 200KΩ potentiometer, so that two The output voltage is equal. (3) Change the input signal frequency and record the output voltage amplitude. Find the frequency value of 0.7 times the output voltage to the maximum voltage, and draw the magnitude of the frequency characteristic curve. 4. Problems and solutions to the debugging process (1) No output voltage: Whether the power supply is turned on; whether the regulator tube is reversed or the model is wrong; the input end has a signal. (2) The magnification is not correct: the feedback resistor and the inverse-phase resistance resistance value are incorrect.
Second, the main technical indicators of the design and production of power amplifiers are as follows. Output power: 2 × 12W; frequency response: 50Hz ~ 20kHz; distortion: ≤ 0.5%. 1. Circuit Design This item uses integration TDAL521 design and produces a power low frequency power amplifier. TDA1 521 is a high-quality amplifier integrated circuit with a nine-legged number of in-line plastic packages, with large output power, small variation, and no impact of the switch machine without impact and reliable overheating short-circuit protection. The output power is 2 × 12 W, the distortion is ≤0.1%. TDAL521A can be powered in power supply or power supply with a single source. When the dual power supply is powered, two audio output capacitors can be saved, and the high and low sound quality is better. When the single power supply is powered, the power filter capacitor should be as close as possible to the power supply of the integrated circuit to avoid self-exchancing of the circuit. When making it, you must put a heat sink to the integrated block to energize the audio, otherwise it is easy to damage the integrated block. The heat sink cannot be less than 200mm × 100 mm × 2 mm. 2. The circuit production power amplifier circuit is shown below. This circuit uses a dual power supply. Note: (1) The TDAL521 power supply must not be reversed, otherwise the circuit will be burned. (2) The heat sink is large enough, not less than 200mm × 100 mm × 2 mm. (3) The speaker does not sell in the circuit, and the output terminal is output when assembled. (4) In order to reduce noise, the power amplifier circuit and the pre-amplifier are soldered on the same piece of board, and the output of the front amplifier is as close as possible.
3. Circuit debug (1) Connect the power amplifier to the front amplifier. Two channel inputs input the same AC small signal (UI = 10mv, f = 1 kHz) to measure two output voltage, observe the range of output voltage changes; (2) Adjust the double potentiometer. The maximum lossless voltage of the output is measured; (3) The communication band of the measurement circuit.
Third, the assembly of the megaphone
1. When the auxiliary circuit is assembled, there is a need to add some auxiliary circuits: (1) Input terminal white: Left channel red: right channel (2) output terminal left and right channels, black ends; (3) switches, indicators, insurance as follows Down shown.
2. The connection line is reduced to reduce noise, ensuring that the signal is not distorted, the signal input connection line and the dual potentiometer cable are used to shield line. 3. Shell (1) Input Terminal, Volume Adjustment End, Indicator, Switch Fixed in the front panel; output terminals, insurance, and power cords are fixed in the rear panel. (2) When you look into your eyes, the outer casing should be aligned with the board. The assembled megaphone is shown below. 4. Easy to have problems and solutions in the debugging of megaphones (1) No sound: the power supply is not turned on; the DC voltage regulator is not working; the circuit connection is incorrect. (2) Noise: unscrupulous shield line. By making and debugging the megaphone circuit, the following capability goals are achieved: (1) Correct identification, detection, and selection of resistors, capacitors, diodes, triodes, integrated tripod regulators, integrated op amps, integrated power plants. (2) Can read the schematic of practical electronic circuitry. (3) The utility circuit can be welded according to the circuit schematic. (4) Proficiency in the use of multimeters, signal generator analog oscillators and other electronic measuring instruments for testing of basic parameters. (5) It is possible to commission the circuit of the production to meet the design requirements.
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